Make ReadOnlyProperty and PropertyDelegateProvider fun interfaces

libraries/stdlib/api/js-v1/kotlin.properties.kt

@@ -19,11 +19,11 @@ public abstract class ObservableProperty<V> : kotlin.properties.ReadWritePropert
 }
 
 @kotlin.SinceKotlin(version = "1.4")
-public interface PropertyDelegateProvider<in T, out D> {
+public fun interface PropertyDelegateProvider<in T, out D> {
     public abstract operator fun provideDelegate(thisRef: T, property: kotlin.reflect.KProperty<*>): D
 }
 
-public interface ReadOnlyProperty<in T, out V> {
+public fun interface ReadOnlyProperty<in T, out V> {
     public abstract operator fun getValue(thisRef: T, property: kotlin.reflect.KProperty<*>): V
 }
 

libraries/stdlib/api/js/kotlin.properties.kt

@@ -19,11 +19,11 @@ public abstract class ObservableProperty<V> : kotlin.properties.ReadWritePropert
 }
 
 @kotlin.SinceKotlin(version = "1.4")
-public interface PropertyDelegateProvider<in T, out D> {
+public fun interface PropertyDelegateProvider<in T, out D> {
     public abstract operator fun provideDelegate(thisRef: T, property: kotlin.reflect.KProperty<*>): D
 }
 
-public interface ReadOnlyProperty<in T, out V> {
+public fun interface ReadOnlyProperty<in T, out V> {
     public abstract operator fun getValue(thisRef: T, property: kotlin.reflect.KProperty<*>): V
 }
 

libraries/stdlib/src/kotlin/properties/Interfaces.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -16,7 +16,7 @@ import kotlin.reflect.KProperty
  * @param T the type of object which owns the delegated property.
  * @param V the type of the property value.
  */
-public interface ReadOnlyProperty<in T, out V> {
+public fun interface ReadOnlyProperty<in T, out V> {
     /**
      * Returns the value of the property for the given object.
      * @param thisRef the object for which the value is requested.
@@ -63,7 +63,7 @@ public interface ReadWriteProperty<in T, V> : ReadOnlyProperty<T, V> {
  * @param D the type of property delegates this provider provides.
  */
 @SinceKotlin("1.4")
-public interface PropertyDelegateProvider<in T, out D> {
+public fun interface PropertyDelegateProvider<in T, out D> {
     /**
      * Returns the delegate of the property for the given object.
      *

libraries/stdlib/test/properties/delegation/DelegationTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -64,3 +64,27 @@ class VetoablePropertyTest {
         assertFalse(result, "fail4: result should be false")
     }
 }
+
+private typealias ReadOnlyPropertyDelegateProvider<T, V> =
+        PropertyDelegateProvider<T, ReadOnlyProperty<T, V>>
+
+class DelegationInterfacesTest {
+    val a by ReadOnlyProperty { _, property -> property.name }
+
+    private val delegatedToProvider = mutableListOf<String>()
+    private val provider = ReadOnlyPropertyDelegateProvider { thisRef: DelegationInterfacesTest, property ->
+        val index = thisRef.delegatedToProvider.size
+        thisRef.delegatedToProvider.add(property.name)
+        ReadOnlyProperty { _, prop -> "${prop.name} is numbered $index" }
+    }
+
+    val b by provider
+    val c by provider
+
+    @Test fun doTest() {
+        assertEquals("a", a)
+        assertEquals(listOf("b", "c"), delegatedToProvider)
+        assertEquals("b is numbered 0", b)
+        assertEquals("c is numbered 1", c)
+    }
+}